Acute Kidney Injury (AKI) is a common problem that affects 67% of patients admitted to the intensive care unit (ICU). AKI is associated with much worse patient outcomes including increased risk of death and the requirement for long-term dialysis. Patients who have more severe forms of AKI often require Renal Replacement Therapy (RRT), a form of dialysis. It is unclear when RRT should be started – earlier RRT may theoretically be better, however it does have its own complications and adds $3000/day to treatment costs. The Timing of Initiation of Renal Support in Acute Kidney Injury (STARRT-AKI) Trial is the largest study of RRT ever undertaken in the ICU and will investigate if early commencement of RRT reduces the risk of dying for patients with AKI. This global study will enroll 2866 patients from 80 ICUs in NZ, Australia, Canada, China and Europe including 400 patients in NZ.